Semiconductor device

ABSTRACT

To provide a semiconductor device capable of preventing the bowing of the substrate, and having a semiconductor layer of a III-V group compound of a nitride system with excellent crystallinity.  
     The semiconductor layer of the III-V group compound of the nitride system whose thickness is equal to or less than 8 μm, is provided onto a substrate made of sapphire. This reduces the bowing of the substrate due to differences in a thermal expansion coefficient and a lattice constant between the substrate and the semiconductor layer of the III-V group compound of the nitride system. An n-side contact layer forming the semiconductor layer of the III-V group of the nitride system has partially a lateral growth region made by growing in a lateral direction from a crystalline part of a seed crystal layer. In the lateral growth region, dislocation density restricts low, therefore, regions corresponding to the lateral growth region of each layer formed onto the n-side contact layer has excellent crystallinity.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor device includinga semiconductor layer made of a semiconductor of a III-V group compoundof a nitride system.

[0003] 2. Description of the Related Art

[0004] The semiconductor of the III-V group compound of the nitridesystem such as a GaN mixed crystal, a AlGaN mixed crystal or a GaInNmixed crystal is a direct transition semiconductor material, and at thesame time, has a characteristic in such that its forbidden band widthspreads from 1.9 eV to 6.2 eV. For this reason, these semiconductors ofthe III-V group compound of the nitride system can obtain light emissionfrom a visible range to an ultra violet range, therefore, it isnoteworthy for a material making a semiconductor light-emitting devicesuch as a semiconductor laser diode (LD) or a laser emitting diode(LED). In connection with this, the semiconductor of the III-V groupcompound of the nitride system is focused attention as a material makingan electron device because of its fast saturation electron speed and itslarge break-down field.

[0005] In general, the semiconductor device using the semiconductor ofthe III-V group compound of the nitride system has a structure such thatlayers of the semiconductor of the III-V group compound of the nitridesystem grown with a MOCVD (Metal Organic Chemical Vapor Deposition)method and a MBE (Molecular Beam Epitaxy) method, are stackedsequentially. As for the substrate, generally, materials whose qualityis different from that of the semiconductor of the III-V group compoundof the nitride system are employed and a sapphire (A1 ₂O₃) substrate ismainly employed. Conventionally, in such a semiconductor device, a totalthickness of the semiconductor of the III-V group compound of thenitride system becomes thicker to obtain the semiconductor of the III-Vgroup compound of the nitride system with excellent crystallinity, whichmaintains and enhances electrical or optical device characteristics. Thesemiconductor of the III-V group compound of the nitride system withexcellent crystallinity can be obtained by growing under hightemperature (in case of GaN, the temperature is about 1000° C.).

[0006] However, sapphire and the semiconductor of the III-V groupcompound of the nitride system are different in a lattice constant andhas a large difference in a thermal expansion coefficient. For thisreason, when growing the semiconductor of the III-V group compound ofthe nitride system, bowing of the sapphire substrate is caused. Thebowing of the sapphire substrate is like to be larger when growing thesemiconductor of the III-V group compound of the nitride system thickeror when growing under high temperature. The bowing of the substratecauses fractures in the sapphire substrate and the bowing of thesemiconductor layer of the III-V group compound of the nitride system,which fails in stability in a manufacturing process significantly. Inaddition, temperature of the substrate when growing the semiconductor ofthe III-V group compound of the nitride system becomes unstable, andthen a composition of the semiconductor of the III-V group compound ofthe nitride system grown thereon becomes heterogeneous depending ranges,which consequently gives damage to controllability in a manufacturingprocess. Specifically, when growing the GaInN mixed crystal as an activelayer of a light-emitting device using the semiconductor of the III-Vgroup compound of the nitride system, a taken-in-amount of indium (In)changes. As a result of this, variation in an oscillation wavelengthoccurs so that a light-emitting effective area capable of oscillating aspecific wavelength, becomes narrow.

[0007] Such problems can be solved by using a substrate made of thesemiconductor of the III-V group compound of the nitride system such asGaN. However, for using this kind of the substrate, there are problemsin that a manufacturing cost and a size of the substrate, then it hasnot been commercialized yet. Accordingly, in a recent situation, thebowing of the substrate is a problem to be solved urgently.

[0008] In recent years, as for growing a crystal of the semiconductor ofthe III-V group compound of the nitride system, several technique toreduce density of the penetration dislocation (a defect such that adislocation defect is propagated and penetrated in crystals; See FIGS. 5and 9) are suggested. One of the techniques is to form an opening suchthat a trench in a seed crystal of the semiconductor of the III-V groupcompound of the nitride system formed on the substrate, and then acrystal is grown in a lateral direction from a side wall surfacecorresponding to the opening of the seed crystal. As for othertechniques, there is a technique such that a belt-shaped mask is formedonto the semiconductor layer of the III-V group compound of the nitridesystem which becomes an underlying layer, and the semiconductor of theIII-V group compound of the nitride system is selectively grown in alateral direction thereon. With such techniques, it is desired that thesemiconductor of the III-V group compound of the nitride system withexcellent crystallinity is grown and device characteristics areenhanced. However, even if with these techniques, the above-mentionedbowing of the substrate is caused. Accordingly, reduction of the bowingof the substrate is urgent necessity for enhancing productivity anddevice characteristics.

[0009] Other and further objects, features and advantages of theinvention will appear more fully from the following description.

SUMMARY OF THE INVENTION

[0010] The invention has been achieved in consideration of the aboveproblems and its object is to provide a semiconductor device capable ofpreventing bowing the substrate and having a semiconductor layer of aIII-V group compound of a nitride system with excellent crystallinity.

[0011] A semiconductor device according to the present inventioncomprises a semiconductor layer made of a semiconductor of a III-V groupcompound of a nitride system containing at least one kind element amonga III group element and at least nitride among a V group element on oneside of the substrate, and the semiconductor layer partly has a lateralgrowth region made by growing the semiconductor of a III-V groupcompound of a nitride system in a lateral direction, then a thickness ofthe semiconductor layer is equal to or less than 8 μm.

[0012] In a semiconductor device according to the present invention, thesemiconductor layer having a lateral growth region is equal to or lessthan 8 μm, so that the semiconductor is excellent in crystallinity andat the same time, bowing of the substrate can be restricted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] These and other objects and features of the present inventionwill become clear from the following description of the preferredembodiments given with reference to the accompanying drawings, in which:

[0014]FIG. 1 is a section view showing a configuration of a main part ofa semiconductor laser diode relative to a first embodiment of thepresent invention;

[0015]FIG. 2A is a section view for describing a method of manufacturingthe semiconductor laser diode shown in FIG. 1;

[0016]FIG. 2B is a section view for describing a method of manufacturingthe semiconductor laser diode following to FIG. 2A;

[0017]FIG. 2C is a section view for describing a method of manufacturingthe semiconductor laser diode following to FIG. 2B;

[0018]FIG. 3 is a section view for describing an advantage ofappropriately choosing a width of a crystalline part and an opening partof the semiconductor laser diode shown in FIG. 1;

[0019]FIG. 4 is a section view for describing manufacturing processesfollowing to FIG. 2C;

[0020]FIG. 5 is a diagram showing a part of the semiconductor laserdiode shown in FIG. 1;

[0021]FIG. 6 is a section view for describing manufacturing processesfollowing to FIG. 4;

[0022]FIG. 7 is a section view for describing manufacturing processesfollowing to FIG. 6;

[0023]FIG. 8 is a section view showing a configuration of a main part ofa semiconductor laser diode relative to a second embodiment;

[0024]FIG. 9 is a diagram showing a part of the semiconductor laserdiode shown in FIG. 8;

[0025]FIG. 10 is a view showing a relationship between a half-breadthvalue of a locking curb in an X-ray diffraction and a thickness of GaNlayers of the semiconductor laser diode obtained by Examples 1-5 andComparative examples 1-5 of the present invention;

[0026]FIG. 11 is a section view showing a configuration of a main partof a semiconductor laser diode relative to other modifications of thesemiconductor laser diode shown in FIG. 1;

[0027]FIG. 12 is a diagram showing a part of the semiconductor laserdiode shown in FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] Hereinafter, embodiments of the present invention will bedescribed by referring drawings in detail.

[0029]FIG. 1 is a view showing a configuration of a main part of asemiconductor laser diode as a semiconductor device relative to a firstembodiment of the present invention. This semiconductor laser diode hasa structure on a substrate 11 such that a seed crystal layer 22, an-side contact layer 23, a n-side clad layer 24, a n-side guide layer25, an active layer 26, a p-type guide layer 27, a p-type clad layer 28and a p-side contact layer 29 are stacked as a semiconductor layer of aIII-V group compound of the nitride system 20 (herein after it isreferred to as a semiconductor layer 20) in this order with a bufferlayer, which is a part of the semiconductor layer 20, in between. Here,the semiconductor of the III-V group compound of the nitride systemcontains at least, one kind element among a III group element such asgallium (Ga), aluminum (Al), boron (B) or indium (In) and at leastnitride (N) among a V group element.

[0030] A p-side electrode 31 is formed onto the p-side contact layer 29.The n-side contact layer 23 partially has regions where the n-type cladlayer 24, the n-type guide layer 25, the active layer 26, the p-typeguide layer 27, the p-type clad layer 28 and the p-side contact layer 29are not formed thereon. An insulating layer 12 is provided with sides ofthe above-mentioned layers and surfaces of the p-type clad layer 24 andthe n-side contact layer 23. An n-side electrode 32 is provided onto then-side contact layer 23 with an opening 12 a provided in the insulatinglayer 12 in between.

[0031] The substrate 11 is made of a material whose thermal expansioncoefficient is different from that of the semiconductor layer 20, forexample, 80-μm-thickness sapphire. The buffer layer 21 and the like areformed onto a c face of the substrate 11. A concave part 11B is providedin a region corresponding to an opening part 22B of the seed crystallayer 22, which will be described later. A preferable depth of theconcave part 11B is equal to or more than 100 nm.

[0032] A total thickness of layers forming the semiconductor layer 20 isequal to or less than 8 μm, because such layers can reduce the bowing ofthe substrate 11 caused by differences in the thermal expansioncoefficient or in a lattice constant between the substrate 11 and thesemiconductor layer 20. More preferably, the total thickness of thesemiconductor layer 20 is within a range between equal to or more than 4μm and equal to or less than 8 μm. As for the reason of such thickness,if thickness is less than 4 μm, element characteristics are degraded bypoor crystallinity.

[0033] Specifically, the buffer layer 21 is within a range of 0.01 μm to0.05 μm in a stacked direction (hereinafter it is referred to as athickness), and is made of undope-GaN. This buffer layer 21 is made of acrystal similar to amorphous, and is a core when growing thesemiconductor layer 20. Additionally, the buffer layer 21 has anaperture part 21B, which is provided in stripes with a predeterminedinterval of about from few μm to 10-odd μm. That is, in this case, acrystal of undope-GaN is also provided in stripes with a predeterminedinterval in between.

[0034] The seed crystal layer 22 is stacked onto the buffer layer 21,and has a crystalline part 22A made of a crystal of the semiconductor ofthe III-V group compound of the nitride system and an opening part 22Bcorresponding to a concave part 11B of the buffer layer 21. A crystal ofundope-GaN whose thickness is within a range of 0.5 μm to 4.0 μm or acrystal of n-type GaN doped silicon (Si) as n-type impurity may be aspecific example of the crystalline part 22A. Here, the seed crystallayer 22 corresponds to one specific example of a first crystallinelayer of the invention. The opening part 22B corresponds to one specificexample of a trench part of the invention.

[0035] The n-side contact layer 23 is made of n-type GaN doped siliconas n-type impurity and partially has a lateral growth region by growingin a lateral direction from the crystalline part 22A of the seed crystallayer 22. A preferable thickness of the n-side contact layer 23 is equalto or less than 6.0 μm, because such thickness reduces the bowing of thesubstrate 11, much more, thermal distribution of the substrate 11 can bemore stable when stacking each of layers forming the semiconductor layer20. Here, the n-side contact layer 23 corresponds to a specific exampleof a second crystalline layer of the present invention.

[0036] The n-type clad layer 24 is, for example, within a range of 0.7μm to 1.2 μm and is made of an n-type AlGaN mixed crystal (for instance,Al_(0.08)Ga_(0.92)N) doped silicon as n-type impurity. The n-type guidelayer 25 is, for example, within a range of 0.08 μm to 0.12 μm and ismade of n-type GaN doped silicon as n-type impurity. The active layer 26is, for example, within a rage of 0.02 μm to 0.04 μm and has a multiplequantum well structure. This structure comprises a well layer and abarrier layer formed by a GaInN mixed crystal layer having differentcomposition respectively. respectively.

[0037] The p-type guide layer 27, is for example, within a range of 0.08μm to 0.12 μm and is made of p-type GaN doped magnesium (Mg) as p-typeimpurity. The p-type clad layer 28 is, for example, within a range of0.3 μm to 0.7 μm and is made of a p-type AlGaN mixed crystal dopedmagnesium as p-type impurity. The p-side contact layer 29 is, forexample, within a range of 0.05 μm to 0.1 μm and is made of p-type GaNdoped magnesium as p-type impurity. Here, for electric currentrestriction, a part of the p-side contact layer 29 and the p-type cladlayer 28 is formed in a narrow belt shape (so-called laser stripe; inFIG. 1, a belt shape extends in a vertical direction relative to a paperof FIG. 1). This laser stripe is provided in a range of the opening part22B of the seed crystal layer 22 thereon, for example.

[0038] The p-side electrode 31 is sequentially stacked palladium (Pd),platinum (Pt) and gold (Au) from a side of the p-side contact layer 29and is electrically connected to the p-side contact layer 29. On theother hand, the n-side electrode 32 is sequentially stacked titanium(Ti), aluminum (Al), platinum (Pt), and gold (Au) and is electricallyconnected to the n-side contact layer 23.

[0039] In this semiconductor laser diode, for instance, a pair of sidesvertical to a longitudinal direction of the p-side electrode 31 is anend surface of a resonator. A pair of reflective mirrors (unillustrated)is respectively formed in the pair of an end surface of a resonator.

[0040] Next, a method of manufacturing the semiconductor laser diodewill be explained.

[0041] In the present embodiment, as shown in FIG. 2A, the substrate 11whose thickness is about 430 μm and made of sapphire, is prepared. Withthe MOCVD method, the semiconductor layer 20 is grown onto the c face ofthe substrate 11 in order to become a thickness equal to or less than 8μm. Specifically, the semiconductor layer 20 is grown as describedhereinafter.

[0042] First, a growth layer 21 a is grown in a range of 0.01 μm to 0.05μm in order to form the buffer layer 21. In this case, a temperature ofthe substrate 11 is set, for example, at 520° C. Then, the temperatureis elevated at 1000° C. and undope-GaN or n-type GaN doped silicon isgrown in a range of 0.5 μm to 4.0 μm onto the growth layer 21 a for abuffer layer so as to form a growth layer 22 a in order to form a seedcrystal layer 22. After this, for instance, with a CVD (Chemical VaporDeposition) method, the insulating film 41 made of silicon nitride orsilicon dioxide is formed on the growth layer 22 a for a seed crystallayer. The growth layer 22 a for a seed crystal layer can be formed ineach of atmospheres: an atmospheric atmosphere, a low-pressureatmosphere, a high-pressure atmosphere. However, among theseatmospheres, for obtaining a crystal with high quality, thehigh-pressure atmosphere is preferable.

[0043] Following this, as shown in FIG. 2B, a photoresist film 42 isformed onto a insulating film 41 and a plurality of striped patternsarranged with a predetermined interval is formed in <1-100> directionsof a GaN crystal (the growth layer 22 a for a seed crystal layer). Then,for example, RIE is carried out with this photoresist film 42 as a maskin order to remove the insulating film 41 selectively. The photoresistfilm 42 is removed after removing the insulting film 41 selectively.Here, <1-100> represents by adding “-” in front of numerals forconvenience in writing, although it generally is represented by drawinga line over numerals.

[0044] After removing the photoresist film 42, as shown in FIG. 2C, RIEis carried out with the insulating film 41 as a mask in order to removeparts, which the growth layer 22 a, the growth layer 21 a and thesubstrate 11 are uncovered with the insulating film 41 to expose thesubstrate 11 in turn. This turns the growth layer 22 a for a seedcrystal layer into the seed crystal layer 22 having the crystalline part22A and the opening part 22B, and turns the growth layer 21 a for abuffer layer into the buffer layer 21 having the aperture part 21B.Additionally, the concave part 11B is formed in the substrate 11.

[0045] As shown in FIG. 3, RIE is carried out in a preferable mannerthat a length L₁ in a width direction of the crystalline part 22A of theseed crystal layer 22 (hereinafter it is referred to as a width) is lessthan 4 μm, and a width L₂ of the crystalline part 22B is equal to orless than 12 μm. Additionally, the width L₁ of the crystalline part 22Ais preferably within a range of 2 μm to 4 μm and the width L₁ of theopening part 12B is within a range of 8 μm to 12 μm. The range of 8μm-12 μm includes 12 μm. Specifically, the seed crystal layer 12 isformed in a manner that the width L₁ is 3 μm and the width L₂ is 9 μm.

[0046] For the reason of determining the width L₂ of the opening part22B is equal to or less than 12 μm, if the width L₂ is more than 12 μm,each of crystals grown in a lateral direction from a side wall surfaceof the crystalline part 22A meets, which causes problems such that agrowth surface of the n-side contact layer 15 takes time to be flattenor a flat growth surface can not be obtained. Additionally, for thereason of determining the width L₂ of the opening part 22B is more than8 μm, the so-called laser stripe whose thickness is a range of 2 μm to 3μm can be formed easily in a part of half of the width L₂ of the openingpart 12B (a part of the width L₂/2 in FIG. 3).

[0047] On the other hand, for the reason of determining the width of thecrystal part 22A is less than 4 μm, if the width is more than 4 μm, acontact area of the seed crystal layer 22 and the substrate 11 becomeslarger, which leads the bowing of the substrate 11 caused by differencesin the thermal expansion coefficient and the lattice constant betweenmaterials contained in the substrate such as sapphire and thesemiconductor of the III-V group compound of the nitride system. If thewidth of the crystalline part 22A is less than 2 μm, the width is toonarrow, which causes difficulties at production.

[0048] After exposing the substrate 11 selectively, as shown in FIG. 4,the insulating 41 is removed by etching. Then, silicon is doped asn-type impurity from the crystalline part 22A of the seed crystal layer22 to grow n-type GaN, which forms the n-side contact layer 23. Here,crystal growth of GaN mainly progresses from a top surface and a sidewall surface of the crystalline part 22A, and in case of regions exceptover the crystalline part 22A, it progresses in a lateral direction (alateral growth region X). In addition, the crystal growth alsoprogresses in a lateral direction from a side wall surface of the bufferlayer 21. As shown in FIG. 5, this propagates penetration dislocation Mlfrom the seed crystal layer 22 (the crystalline part 22A) in a region Yover the crystalline part 22A of the n-side contact layer 23. However,in regions except the region Y (that is, the lateral growth region X),the penetration dislocation M₁ hardly exists because it bends in alateral direction. Growth speed from a side of the crystalline part 22Ais faster than that from a surface of the crystalline part 22A. After alapse of specific time, a crystal of GaN grown from the side of thecrystalline part 22A spreads over and the growth surface is flattened.The penetration dislocation M₂ shown in FIG. 5 is generated such thateach of crystals is grown from the crystalline part 22A and meets in alateral direction.

[0049] As described above, in case that the crystal growth progresses ina lateral direction from the seed crystal layer 22 and the buffer layer21, it may slightly progress in a direction of a side of the substrate11, not to the just right. However, in the present embodiment, a part ofthe substrate 11 is etched to provide the concave part 11B, which canprevent a defect caused by contact of grown crystals to the substrate11. In addition, a crystal with less crystal disorientation, can begrown.

[0050] As has been described, crystals obtained by the above-mentionedmethod can gain a high quality compared with crystals obtained by otherchemical vapor deposition methods. Hence, in the present embodiment,even if a thickness of the semiconductor layer 20 becomes thinner, eachof layers except the buffer layer 21 comprising the semiconductor layer20 is excellent in crystallinity.

[0051] After forming the n-side contact layer 23, as shown in FIG. 6, onthe n-side contact layer 23, with the MOCVD method, for example, then-type clad layer 24 is grown in a range of 0.7 μm to 1.2 μm, the n-typeguide layer 25 is grown in a range of 0.08 μm to 0.12 μm, and then theactive layer 26 is grown in a range of 0.02 μm to 0.04 μm, further, thep-type guide layer is grown in a range of 0.08 μm to 0.12 μm, the p-typeclad layer 28 is grown in a range of 0.3 μm to 0.7 μm, and finally, thep-side contact layer 29 is grown in a range of 0.05 m to 0.1 μm. Wheneach of layers is grown, a temperature of the substrate 11 is adjustedsuitably at about 750° C.-1100° C. respectively.

[0052] A total thickness of the buffer layer 21, the n-side contactlayer 23, the n-type clad layer 24 and the n-type guide layer 25 is sothin that the bowing of the substrate 11 is restricted when the n-typeguide layer 25 is formed. Accordingly, when forming the active layer 26made of a GaInN mixed crystal thereon, the temperature of the substrate11 keeps stable, thus, a fixed amount of indium is taken in. Therefore,compositions of each of well layers in the active layer 26 andcompositions of each of barrier layers are homogeneous without change inevery region.

[0053] Additionally, the penetration dislocation M₁ is like to bepropagated slightly spreading in a radiant way in a growth direction ofthe semiconductor layer 20. In the present embodiment, the totalthickness of the semiconductor layer 20 is equal to or less than 8 μm sothat the spread of the above-mentioned penetration dislocation M₁ can besmaller than conventional one.

[0054] When the MOCVD method is carried out, the gases described laterare employed respectively. Trimethylgallium ((CH₃)₃Ga) is employed assource gas for gallium. Trimethylaluminum ((CH₃)₃Al) is employed assource gas for alminum. Trimethylindium ((CH₃)₃In) is employed as sourcegas for indium. Ammonia (NH₃) is employed as source gas for nitride. Inaddition, monosilane (SiH₄) is employed as source gas for silicon.Bis=cycropentadienyl magnesium ((C₅H₅)₂Mg) is employed as source gas formagnesium.

[0055] After growing the semiconductor layer 20, a part of the p-sidecontact layer 29, the p-type clad layer 28, the p-type guide layer 27,the active layer 26, the n-type guide layer 25, the n-type clad layer 24and the n-side contact layer 23 is etched in turn to expose the n-sidecontact layer 23 on a surface. Following this, an unillustrated mask isformed to be used for selectively etching a part of the p-side contactlayer 29 and the p-type clad layer 28 with RIE (a Reactive Ion Etchingmethod), and an upper part of the p-type clad layer 28 and the p-sidecontact layer 29 become a narrow belt shape (a ridge shape).

[0056] In this case, the unillustrated mask is preferably disposed in aregion corresponding to the width L₂/2 shown in FIG. 3. Sincepenetration dislocation M₂ is generated by meeting each of crystalsgrown in a lateral direction from the crystalline part 12 and exists inthe general center of the width of the opening part 22B and, so-calledlaser stripe which becomes a radiative range, is formed from a part of aboundary surface of the opening part 12A and the crystalline part 22A tohalf of the width L₂ the opening part 12B.

[0057] After this, as shown in FIG. 7, the insulating layer 12 made ofsilicon dioxide (SiO₂) is formed with a deposition method in a wholeexposed surface. Then, an unillustrated resist film is formed thereon.With RIE, the insulating layer 12 is exposed by selectively removing aregion corresponding to the above-mentioned ridge shape in the resistfilm. Following this, by removing the exposed surface of the insulatingfilm 12, the p-side contact layer 29 is exposed on a surface to coverregions except the surface of the p-side contact layer 29 with theinsulating layer 12.

[0058] The p-side electrode 31 is formed by depositing palladium,platinum, and gold in turn on a surface and in a vicinity of the p-sidecontact layer 29. After forming the opening 12 a in a region on then-side contact layer of the insulating layer 12, the n-side electrode 32is formed by depositing titanium, aluminum, platinum and gold in turn tothe opening 12 a. Then, the substrate 11 is ground in a manner to be 80μm of thickness, for example. Here, the bowing of the substrate 11 isrestricted so that it is ground easily. Finally, the substrate 11 iscleaved in a predetermined width perpendicular to a longitudinaldirection of the p-side electrode 31, and on a cleavage surface, theunillustrated reflective mirrors are formed.

[0059] In the semiconductor laser diode, after a predetermined voltageis applied to the p-side electrode 31 and the n-side electrode 32, thecurrent is applied to the active layer 26, which generates radiationcaused by an electron-hole combination. A composition of a GaInN mixedcrystal of each well layer and each barrier layer forming the activelayer 26 are so homogenous that an oscillation wavelength is uniform.

[0060] As described above, in the semiconductor laser diode relative tothe present embodiment, the semiconductor layer 20 whose total thicknessis equal to or less than 8 μm is provided, which achieves restriction ofthe bowing of the substrate 11 caused by differences in the thermalexpansion coefficient or the lattice constant between the substrate 11and the semiconductor layer 20. Additionally, the bowing of thesemiconductor layer 20 accompanying by the bowing of the substrate 11can also be restricted. Consequently, before and after manufacturing,this prevents fractures of the substrate 11 and the semiconductor layer20.

[0061] Further, accompanying by reduction of the bowing of thesubstrate, when growing the semiconductor layer 20, the temperature ofthe substrate 11 becomes stable. Therefore, especially, when forming theactive layer 26 made of a GaInN mixed crystal, the fixed amount ofindium taken in, thereby each of well layers and barrier layerscomprising the active layer 26 become homogeneous in composition. Hence,when activating, an oscillation wavelength becomes uniform, whichattains a semiconductor laser diode with high repeatability. Inaddition, a position of forming a radiative range is not limited andflexibility in production can be attained, which contributes toproductivity.

[0062] Furthermore, the n-side contact layer 23 is formed by using thecrystalline part 22A and has the lateral growth region X so that then-side contact layer 23, the n-type clad layer 24, the n-type guidelayer 25, the active layer 26, the p-type guide layer 27, the p-typeclad layer 28 and the p-side contact layer 29, those layer are formed onthe n-side contact layer 23, have high crystallinity in the lateralgrowth region X. For the reason of this, if so-called laser stripe isformed in the lateral growth region X (specifically, a regioncorresponding to half of the width L₂ of the opening part 22B ),degradation caused by applying a voltage is hardly occurred, thereby,the semiconductor laser diode with long life can be obtained.

[0063] When manufacturing, a crystal of the semiconductor of the III-Vgroup compound of the nitride system whose thickness is equal to or lessthan 8 μm, is grown from the crystalline part 22A of the seed crystallayer 22 having the opening part 22B. Therefore, in the lateral growthregion X, a high quality crystal in which the penetration dislocation M₁hardly exist, is grown, and even if the penetration dislocation M₁slightly spreads in a crystal growth direction, since a thickness of agrown crystal is not thick enough, the penetration dislocation M₁affects less. This increases an excellent region in crystallinity withlow-density of the penetration dislocation M₁, and in a latter process,a region capable of forming a radiative range increases. Flexibility inproduction can be enhanced, and the semiconductor laser diode with highquality and excellent repeatability can be obtained easily.

[0064] In connection with this, the bowing of the substrate 11 isrestricted, which reduces a burden to the semiconductor layer 20 and asa result of this, manufacturing yields can be enhanced.

[0065] The semiconductor laser diode is utilized as a semiconductorlight-emitting apparatus by mounting on a heat sink through a submount.The heat sink is for dissipating heat generated by the semiconductorlaser diode. In the semiconductor laser diode of the present embodiment,as described above, the bowing of the submount 11 and accompanying bythis, the bowing of the semiconductor layer 20 are reduced. As a resultof this, the contact among the submount, the heat sink and thesemiconductor laser diode increases, then the heat generated by thesemiconductor laser diode when actuating can be dissipated well. Thiscan prevent an increase in threshold current of the semiconductor laserdiode and a decrease in a radiative output due to thermal interference.As a result of this, high quality can be maintained for a long time andthe long-life semiconductor laser diode can be achieved.

Second Embodiment

[0066]FIG. 8 is a view showing a configuration of a main part of asemiconductor laser diode as a semiconductor device relative to a secondembodiment of the present invention. The semiconductor laser diode hasthe same configuration, work and effect as the semiconductor laser diodeexcept in that a semiconductor layer of a III-V group compound of anitride system 60 (herein after it is referred to as a semiconductorlayer 60) is included in replace of the semiconductor layer 20 relativeto the first embodiment and further a mask part 64 is also included.Therefore, the same configurations has the same references and thedetailed explanation is omitted.

[0067] The semiconductor layer 60 has an underlying layer 61, a coveredgrowth layer 62 and an n-side contact layer 63 in replace of the bufferlayer 21, the seed crystal layer 22 and the n-side contact layer 23 ofthe semiconductor layer 20 respectively. The total thickness of thesemiconductor layer 60 is equal to or less than 8 μm and a range ofequal to or more than 4 μm to equal to or less than 8 μm is preferableas the same as the first embodiment.

[0068] The underlying layer 61 is provided adjacent to the substrate 11within a range of 0.5 μm to 2.0 μm and made of a crystal of undope-GaN.

[0069] The mask part 64 is provided onto the underlying layer 61 with0.1 μm of thickness and made of dielectrics such as silicon nitride(Si₃N₄) or silicon dioxide. The mask part 64 is a plurality of masksdisposed in a predetermined interval. The plurality of masks is extendedin a belt shape vertical to a sheet in FIG. 9 with an opening inbetween. On the mask part 64, the covered growth layer 62 is selectivelygrown in a lateral direction (a direction vertical to a stackingdirection), which shields propagation of the penetration dislocation M₁(See FIG. 8) from the underlying layer 61.

[0070] The covered growth layer 62 is within a range of 0.5 μm to 2.0 μmand made of undope-GaN. The covered growth layer 62 selectively has thelateral growth region X (See FIG. 9) grown in a lateral direction usingthe mask part 64. The n-side contact layer 63 is within a range of 2.0μm to 5.0 μm and made of n-type GaN doped silicon as n-type impurity.

[0071] Next, a method of manufacturing of the semiconductor laser diodewill be described hereinafter.

[0072] First, the substrate 11 made of sapphire is prepared. With theMOCVD method, the buffer layer 21 made of undope-GaN and the underlyinglayer 61 are grown in turn. In the underlying layer 61, the penetrationdislocation M₁ illustrated with a thin line as shown in FIG. 9,typically exists. FIG. 9 is a view showing a part of processes in amethod of manufacturing the semiconductor laser diode.

[0073] Following this, with a CVD (Chemical Vapor Deposition) method, asilicon dioxide layer is formed onto the underlying layer 61. Then, anunillustrated resist film is covered on the silicon dioxide layer toform a plurality of parallel belt-shaped resist patterns withphotolithography. By using this, the silicon dioxide layer isselectively removed with etching to form the mask part 64.

[0074] With the MOCVD method, the covered growth layer 62 made ofundope-GaN is grown in the same manner as the underlying layer 61. Atthis moment, firstly, GaN is grown in a manner to fill openings in eachmask of the mask part 64 and is grown in a lateral direction on themask. Accordingly, as shown in FIG. 9, in the region Y where the mask onthe underlying layer 61 is not formed among the covered growth layer 62,the penetration M₁ is generated as the same as the underlying layer 61because the penetration dislocation M₁ is propagated from the underlyinggrowth layer 61. On the other hand, in the region X on the mask partwithin the covered growth layer 62, the penetration dislocation M₁ isgenerated because it is grown in a lateral direction.

[0075] After growing the covered growth layer 62, for example, with theMOCVD method, the n-side contact layer 63 is formed thereon. Processesafter this are the same as the first embodiment. In the n-side contactlayer 63, the n-type clad layer 24, the n-type guide layer 25, theactive layer 26, the p-type guide layer 27, the p-type clad layer 28 andthe p-side contact layer 29, the penetration dislocation M1 is notpropagated in a part corresponding to the lateral growth region X (FIG.9). Therefore, when the upper part of the p-type clad layer 28 and thep-side contact layer 29 are shaped in a ridge shape, if those layers areetched in a manner to leave the region Y (FIG. 9) on the mask part wherethe penetration dislocation M₁ is not propagated, device characteristicsof semiconductor laser diode such as life characteristics can beenhanced since a low-density region of the penetration dislocation M₁(that is, a regeon with excellent crystallinity) become a radiativerange on the above-mentioned layers.

[0076] As described above, in the semiconductor laser diode relative tothe present embodiment, the semiconductor layer 60 whose total thicknessis equal to or less than 8 μm, is provided on the substrate 11 so thatthe bowing the substrate 11 can be restricted as the same as the firstembodiment.

[0077] Additionally, in a region on the mask part 64 formed on theunderlying layer 61, the covered growth layer 62 is disposed. In thecovered growth layer 62, propagation of the penetration dislocation M₁is effectively prevented from the underlying layer 61 with a lateralgrowth, so that a semiconductor of a III-V group compound of a nitridesystem with excellent crystallinity is formed on the region (the lateralgrowth region X) where the propagation of the penetration dislocation M₁is effectively prevented. Hence, device characteristics of thesemiconductor laser diode can be improved by disposing a radiative rangein a part corresponding to the lateral growth region X.

EXAMPLE

[0078] Further, specific examples of the present invention will bedescribed in detail.

Examples 1-5; Evaluation of the GaN Layer

[0079] First, a substrate made of sapphire was prepared. GaN was grownon a c face of the substrate 40 nm with a MOCVD method to form a growthlayer for a buffer layer. Following this, with the same MOCVD method,GaN was grown 2 μm to form a growth layer for a seed crystal layer, andthen, a insulating film made of silicon nitride was formed on the growthlayer for a seed crystal layer with a CVD method.

[0080] Next, a photoresist film was formed on the insulating film and atthe same time, a plurality of patterns with a striped shape was formed.RIE was carried out with the pattern-formed photoresist film as a maskto remove the insulating film selectively. After this, the photoresistfilm was removed.

[0081] After removing the photoresist film, RIE was carried out with theinsulating film as a mask to remove part, which the growth layer for theseed crystal layer, the growth layer for a buffer layer, and thesubstrate were uncovered with the insulating film in turn. Then, thesubstrate was exposed to an interface between the substrate and thegrowth layer for a buffer layer. This formed a seed crystal layer havinga crystalline part and an opening part, and a buffer layer having anaperture part.

[0082] Following this, the insulating film was removed by etching. Withthe MOCVD method, a GaN layer was formed by growing GaN from thecrystalline part of the seed crystal layer. At this moment, in Examples1-5, a thickness of the GaN layer was changed as shown in Table 1. Inaddition, GaN grown from the crystalline part of the seed crystal layerhad a region grown in a lateral direction selectively. TABLE 1 Thicknessof GaN Half-Value Breadth (μm) (arcsec) Example 1 4.0 158 Example 2 5.0124 Example 3 5.0 131 Example 4 7.0 121 Example 5 8.0 139 ComparativeExample 1 10.0  194

[0083] When forming each of layers with the MOCVD method,trimethylgallium was employed as a source gas of gallium and ammonia wasemployed as a source gas of nitride.

[0084] As Comparative example 1 relative to Examples 1-5, the GaN layerwas grown in a similar manner as Example 1-5 except in that a thicknessof the GaN layer was 10 μm. As Comparative examples 2-5 relative toExamples 1-5, the GaN layer was grown as described hereinafter.

[0085] The substrate made of sapphire was prepared. GaN was grown 40 nmon the c face of the substrate with the MOCVD method to form the bufferlayer. After this, on the buffer layer, GaN was grown with the MOCVDmethod to form the GaN layer. In this case, a thickness of the GaN layerwas changed as shown in Comparative examples 2-5. The GaN layer wasgrown in a vertical direction relative to a growth surfacesubstantially. TABLE 2 Thickness of GaN Half-Value Breadth (μm) (arcsec)Comparative Example 2 3.9 222 Comparative Example 3 4.0 215 ComparativeExample 4 4.0 227 Comparative Example 5 5.0 198

[0086] The obtained GaN layers as described above in Examples 1-5 andComparative examples 1-5 were analyzed with an X-ray diffraction method.FIG. 10 is a graph showing a half-value breadth of a locking curve withan X-ray analysis of the obtained GaN layers in Examples 1-5 andComparative examples 1-5. The obtained results are also shown in Tables1 and 2. In FIG. 9, a vertical axis shows a half-value breadth (unit;arcsec), and a horizontal axis shows a thickness of the GaN layer (unit;μm).

[0087] As can be seen in FIG. 10, Tables 1 and 2, a half-value breadthof Example 1 was a smallest value in those of Comparative examples 2-4.A half-value breadth of Example 2 was smaller than that of Comparativeexample 5. As a result of this, it was confirmed that GaN having aregion grown in a lateral direction was excellent in crystallinity.Further, any half-value breadths of Examples 1-5 were smaller than thatof Comparative example 1. This might be caused by the reason that if athickness of the GaN layer was 10 μm, the bowing of the substrateincreased, which caused an increase of deflection in crystals. As aresult described above, in the GaN layer whose thickness was equal to orless than 8 μm and grown in a lateral direction partly, the bowing ofthe substrate was reduced and excellent crystallinity could be achieved.

[0088] Although the detailed describe is omitted here, in case that asemiconductor of a III-V group compound of a nitride system containingat least one kind element among a III group element and nitrideexcluding GaN, is grown, the same results can be obtained.

Example 2; Evaluation of the Semiconductor Laser Diode

[0089] Further, with the MOCVD method, a n-type clad layer, a n-typeguide layer, an active layer, a p-type guide layer, a p-type clad layerand a p-side contact layer were formed onto the GaN layer of Example 2sequentialy. Specifically, an n-type Al_(0.08)Ga_(0.92)N mixed crystaldoped silicon was grown 1.2 μm to form the n-type clad layer and n-typeGaN doped silicon is grown 0.1 μm to form the n-type guide layer. Theactive layer was formed as described hereinafter. First, an N-type GaInNmixed crystal doped silicon is grown 7.0 nm to form the barrier layer,then, an undope-GaInN mixed crystal was grown 3.5 nm to form a welllayer. Finally, the active layer was formed by stacking those layers in3 periods. P-type GaN doped magnesium was grown 0.1 μm to form thep-type guide layer. A p-type Al_(0.08)Ga_(0.92)N mixed crystal was grownin 0.5 μm to form the p-type clad layer. P-type GaN doped magnesium wasgrown 0.1 μm to form the p-side contact layer.

[0090] When forming each of layers with the MOCVD method,trimethylgallium was employed as a source gas of gallium,trimethylaluminum was employed as a source gas of aluminum,trimethylinduim was employed as a source gas of indium, and ammonia isemployed as a source gas of nitride. Monosilane was employed as a sourcegas of silicon, and bis=cycropentadienyl magnesium was employed as asource gas of magnesium.

[0091] After forming the p-side contact layer, the p-side contact layer,the p-type clad layer, the p-type guide layer, the active layer, then-type guide layer, the n-type clad layer and the n-side contact layerwere selectively etched to expose the n-side contact layer on a surface.Following this, a mask was formed parallel to a longitudinal directionof a region where a p-side electrode to be formed in a latter process.With a RIE method by using the mask, a part of the p-side contact layerand the p-type clad layer were selectively etched to shape the upperpart of the p-type clad layer and the p-side contact layer in a narrowbelt shape.

[0092] An insulating layer made of silicon dioxide was formed on thewhole exposed surface of the substrate with a deposition method. Aresist film was formed thereon. Then, RIE was carried out in severaltimes to cover regions except a surface of the p-side contact layer withthe insulating film.

[0093] After this, on a surface and in a vicinity of the p-side contactlayer, palladium, platinum and gold were deposited sequentially to formthe p-side electrode. An opening was formed in a region on the n-sidecontact layer of the insulating layer and titanium, aluminum, platinum,and gold were deposited thereon to form the n-side electrode. Afterthis, the substrate was ground in a manner to be 80 μm of thickness.Finally, the substrate was cleaved vertical to a longitudinal directionof the p-side electrode in a predetermined width, then, a reflectivemirror film was formed onto the cleavage surface to produce thesemiconductor laser diode. As for the above-mentioned Comparativeexample 5, the semiconductor laser diode was also produced as the sameas Example 2.

[0094] Further, a submount and a heat sink were prepared. Thesemiconductor laser diodes of Example 2 and of Comparative example 5were mounted on the heat sink through the submount to assemble asemiconductor laser-light emitting device, and then a life test wascarried out at room temperature. Consequently, the semiconductor laserdiode of Example 2 could achieve a life for over 1000 hours under 20 mWoutput. As compared with this, the semiconductor laser diode ofComparative example 5 obtained a life for over 100 hours under 20 mW.This could be achieved for the reason that the bowing of the submountwas reduced, and accompanying by this, the bowing of each layers made ofthe semiconductor of the III-V group compound of the nitride system wasreduced. Hence, this enhanced a contact among the submount, the heatsink and the semiconductor laser diode, which results in effectivelydissipating heat generated by the semiconductor laser diode.

[0095] As has been described above, the present invention has beenexplained by given the embodiments and examples. The present inventionis not limited by the embodiments and the examples, and manymodifications and variations of the present invention are possible. Forinstance, in the above-mentioned each of embodiments, although thecontact layer and the guide layer were made of GaN, the clad layer wasmade of AlGaN mixed crystal, and the active layer was made of InGaNmixed crystal, these semiconductor layers of the III-V group compound ofthe nitride system may be made of at least one kind element among a IIIgroup element and other semiconductors of a III-V group compoundcontaining nitride. In the second embodiment, the underlying layer 61made of undope-GaN and the covered growth layer 62 was given as anexample, and in the third embodiment, the seed crystal layer 71 made ofundope-GaN was given as an example, these layers also may be made of thesemiconductor of the III-V group compound of the nitride systemexcluding undope-GaN.

[0096] Obviously many modifications and variations of the presentinvention are possible in the light of the above teachings. It istherefore to be understood that within the scope of the appended claimsthe invention may be practiced otherwise than as specifically described.

[0097] Furthermore, although in the above-mentioned each of embodiments,the substrate 11 was made of sapphire, the substrate may be made ofmaterials whose thermal expansion coefficient is different from that ofthe semiconductor of the III-V group compound of the nitride system.Such materials are: silicon carbide (SiC) and spinel (MgAl₂O₄).

[0098] Moreover, in the above-mentioned first embodiment, after removingthe insulating 41, the n-side contact layer 23 was formed. As shown inFIG. 11, the n-side contact layer 23 may be formed without removing theinsulating layer 41 on the seed crystal layer 22. This shields thepenetration dislocation M₁ with the insulating film 41, which preventspropagation of the penetration dislocation M₁ from the seed crystallayer 22. Accordingly, in the n-type contact layer 23, crystal defectshardly exist except the penetration dislocation M₂, which is a cause ofa meet. This can gain the semiconductor layer of the III-V groupcompound of the nitride system with excellent crystallinity. However,preferably, a manufacturing method may be chosen depending on a purposefor use because when growing the n-side contact layer 23, a materialscontained the insulating film 41 is mixed into the n-side contact layer23 as an impurity, which degrades characteristics of a semiconductorlaser diode.

[0099] In the above-mentioned each of embodiments, although it isdescribed that the case where the semiconductor layer 20 and 60 wereformed with the MOCVD method, other chemical vapor deposition methodssuch as a MBE method and a HVPE (hideride chemical vapor deposition)method can be used to form these layers. The HVPE method is a chemicalvapor deposition method such that halogen contributes to transportationor reaction.

[0100] In the above-mentioned each of embodiments, although the n-sidecontact layer 23, the n-type clad layer 24, the n-type guide layer 25,the active layer 26, the p-type guide layer 27, the p-type clad layer 28and the p-side contact layer 29 were sequentially stacked, asemiconductor laser diode having other configurations can be applied tothe present invention. For example, a degradation-preventing layer maybe included between the active layer 26 and the p-type guide layer 27instead of the n-type guide layer 25 and the p-type guide layer 27.Further, in the above-mentioned each of embodiments, although a part ofthe p-type clad layer 28 and the p-side contact layer 29 were shaped ina narrow belt shape for electric current restriction, otherconfigurations may be applied for electric current restriction.Additionally, although the semiconductor laser diode of a ridgewaveguide type combined with a gain waveguide type and a reflectiveintensity waveguide type was described as an example, a semiconductorlaser diode of a gain wave guide type and the semiconductor laser diodeof a reflective intensity waveguide type can be also applied in a likemanner.

[0101] In the above-mentioned first embodiment, although it is describedthat the case where the concave part 11B was provided in the substrate11, the concave part 11B is not always needed to provide. However, ifthe concave part 11B is provided, occurrence of defects when producingand dislocation of a crystal axis can be prevented.

[0102] In addition, in the above-mentioned each of embodiments, althoughthe semiconductor laser diode was given as a semiconductor device, thepresent invention can be applied to other semiconductor devices such asa light-emitting diode or an electric field effect transistor.

[0103] As has been mentioned above, in the semiconductor deviceaccording to the present invention, the lateral growth region isprovided on the substrate and the semiconductor layer whose thickness isequal or less than 8 μm is disposed, so that even if the substrate andthe semiconductor layer has different quality of materials, the bowingof the substrate can be restricted, and the semiconductor layer made ofthe semiconductor of the III-V group compound of the nitride can achievehigh crystallinity.

[0104] While the invention has been described with reference to specificembodiment chosen for purpose of illustration, it should be apparentthat numerous modifications could be made there to by those skilled inthe art without departing from the basic concept and scope of theinvention.

What is claimed is:
 1. A semiconductor device including a semiconductorlayer made of a semiconductor of a III-V group compound of a nitridesystem containing at least one kind element among a III group elementand at least nitride among a V group element on one side of thesubstrate, comprising; the semiconductor layer, which has partly alateral growth region made by growing the semiconductor of the III-Vgroup compound of the nitride system, and whose thickness is equal to orless than 8 μm.
 2. A semiconductor device according to claim 1 , whereinthe semiconductor device comprises a first crystal layer including acrystalline part made of a crystal of the semiconductor of a III-V groupcompound of a nitride system and a trench; and a second crystal layermade of the semiconductor of a III-V group compound of a nitride systemis disposed in a manner to cover the crystalline part of the firstcrystal layer.